Cortex-M SysTick Defines

libopencm3 Defined Constants and Types for the Cortex SysTick More...

Collaboration diagram for Cortex-M SysTick Defines:

Modules
	STK_CSR Values
	STK_RVR Values
	STK_CALIB Values

Macros
#define	STK_CSR   MMIO32(SYS_TICK_BASE + 0x00)
	SysTick Control and Status Register (CSR). More...
#define	STK_RVR   MMIO32(SYS_TICK_BASE + 0x04)
	SysTick Reload Value Register (RVR). More...
#define	STK_CVR   MMIO32(SYS_TICK_BASE + 0x08)
	SysTick Current Value Register (CVR). More...
#define	STK_CALIB   MMIO32(SYS_TICK_BASE + 0x0C)
	SysTick Calibration Value Register(Read Only) (CALIB) Reads the calibration value and parameters for SysTick. More...

Functions
void	systick_set_reload (uint32_t value)
	SysTick Set the Automatic Reload Value. More...
bool	systick_set_frequency (uint32_t freq, uint32_t ahb)
	SysTick Set clock and frequency of overflow. More...
uint32_t	systick_get_reload (void)
	SysTick Read the Automatic Reload Value. More...
uint32_t	systick_get_value (void)
	Get the current SysTick counter value. More...
void	systick_set_clocksource (uint8_t clocksource)
	Set the SysTick Clock Source. More...
void	systick_interrupt_enable (void)
	Enable SysTick Interrupt. More...
void	systick_interrupt_disable (void)
	Disable SysTick Interrupt. More...
void	systick_counter_enable (void)
	Enable SysTick Counter. More...
void	systick_counter_disable (void)
	Disable SysTick Counter. More...
uint8_t	systick_get_countflag (void)
	SysTick Read the Counter Flag. More...
void	systick_clear (void)
	SysTick Clear counter Value. More...
uint32_t	systick_get_calib (void)
	SysTick Get Calibration Value. More...

Detailed Description

libopencm3 Defined Constants and Types for the Cortex SysTick

Version

1.0.0

Author

© 2010 Thomas Otto tommi.nosp@m.@via.nosp@m.dmin..nosp@m.org

Date

19 August 2012

System Control Space (SCS) => System timer register support in the SCS. To configure SysTick, load the interval required between SysTick events to the SysTick Reload Value register. The timer interrupt, or COUNTFLAG bit in the SysTick Control and Status register, is activated on the transition from 1 to 0, therefore it activates every n+1 clock ticks. If you require a period of 100, write 99 to the SysTick Reload Value register. The SysTick Reload Value register supports values between 0x1 and 0x00FFFFFF.

If you want to use SysTick to generate an event at a timed interval, for example 1ms, you can use the SysTick Calibration Value Register to scale your value for the Reload register. The SysTick Calibration Value Register is a read-only register that contains the number of pulses for a period of 10ms, in the TENMS field, bits[23:0].

This register also has a SKEW bit. Bit[30] == 1 indicates that the calibration for 10ms in the TENMS section is not exactly 10ms due to clock frequency. Bit[31] == 1 indicates that the reference clock is not provided.

LGPL License Terms libopencm3 License

Macro Definition Documentation

STK_CALIB

#define STK_CALIB   MMIO32(SYS_TICK_BASE + 0x0C)

SysTick Calibration Value Register(Read Only) (CALIB) Reads the calibration value and parameters for SysTick.

Usage constraints: There are no usage constraints. Configurations Always implemented.

Definition at line 90 of file systick.h.

STK_CSR

#define STK_CSR   MMIO32(SYS_TICK_BASE + 0x00)

SysTick Control and Status Register (CSR).

Controls the system timer and provides status data. Usage constraints: There are no usage constraints. Configurations Always implemented.

Definition at line 66 of file systick.h.

STK_CVR

#define STK_CVR   MMIO32(SYS_TICK_BASE + 0x08)

SysTick Current Value Register (CVR).

Holds the current value of the counter. Usage constraints: There are no usage constraints. Configurations Always implemented.

Definition at line 83 of file systick.h.

STK_RVR

#define STK_RVR   MMIO32(SYS_TICK_BASE + 0x04)

SysTick Reload Value Register (RVR).

Reads or clears the value that will be loaded to the counter. Usage constraints:

• Any write to the register clears the register to zero.
• The counter does not provide read-modify-write protection.
• Unsupported bits are read as zero Configurations Always implemented.

Definition at line 76 of file systick.h.

Function Documentation

systick_clear()

void systick_clear

(

void

)

SysTick Clear counter Value.

The counter value is cleared. Useful for well defined startup.

Definition at line 187 of file systick.c.

References STK_CVR.

systick_counter_disable()

void systick_counter_disable

(

void

)

Disable SysTick Counter.

Definition at line 162 of file systick.c.

References STK_CSR.

systick_counter_enable()

void systick_counter_enable

(

void

)

Enable SysTick Counter.

Definition at line 152 of file systick.c.

References STK_CSR, and STK_CSR_ENABLE.

systick_get_calib()

uint32_t systick_get_calib

(

void

)

SysTick Get Calibration Value.

Returns

Current calibration value

Definition at line 197 of file systick.c.

References STK_CALIB, and STK_CALIB_TENMS.

systick_get_countflag()

uint8_t systick_get_countflag

(

void

)

SysTick Read the Counter Flag.

The count flag is set when the timer count becomes zero, and is cleared when the flag is read.

Returns

Boolean if flag set.

Definition at line 176 of file systick.c.

References STK_CSR, and STK_CSR_COUNTFLAG.

systick_get_reload()

uint32_t systick_get_reload

(

void

)

SysTick Read the Automatic Reload Value.

Returns

24 bit reload value as uint32_t.

Definition at line 66 of file systick.c.

References STK_RVR, and STK_RVR_RELOAD.

systick_get_value()

uint32_t systick_get_value

(

void

)

Get the current SysTick counter value.

Returns

24 bit current value as uint32_t.

Definition at line 108 of file systick.c.

References STK_CVR, and STK_CVR_CURRENT.

systick_interrupt_disable()

void systick_interrupt_disable

(

void

)

Disable SysTick Interrupt.

Definition at line 142 of file systick.c.

References STK_CSR.

systick_interrupt_enable()

void systick_interrupt_enable

(

void

)

Enable SysTick Interrupt.

Definition at line 132 of file systick.c.

References STK_CSR, and STK_CSR_TICKINT.

systick_set_clocksource()

void systick_set_clocksource

(

uint8_t

clocksource

)

Set the SysTick Clock Source.

The clock source can be either the AHB clock or the same clock divided by 8.

Parameters

[in]

clocksource

uint8_t. Clock source from Clock source selection.

Definition at line 121 of file systick.c.

References STK_CSR, and STK_CSR_CLKSOURCE.

Referenced by systick_set_frequency().

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systick_set_frequency()

bool systick_set_frequency	(	uint32_t	freq,
		uint32_t	ahb
	)

SysTick Set clock and frequency of overflow.

This function sets the systick to AHB clock source, and the prescaler to generate interrupts with the desired frequency. The function fails, if the frequency is too low.

Parameters

[in]	freq	uint32_t The desired frequency in Hz
[in]	ahb	uint32_t The current AHB frequency in Hz

Returns

true, if success, false if the desired frequency cannot be set.

Definition at line 81 of file systick.c.

References STK_CSR_CLKSOURCE_AHB, STK_CSR_CLKSOURCE_AHB_DIV8, STK_RVR_RELOAD, systick_set_clocksource(), and systick_set_reload().

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systick_set_reload()

void systick_set_reload

(

uint32_t

value

)

SysTick Set the Automatic Reload Value.

The counter is set to the reload value when the counter starts and after it reaches zero.

Note

The systick counter value might be undefined upon startup. To get predictable behavior, it is a good idea to set or clear the counter after set reload.

See also

systick_clear

Parameters

[in]

value

uint32_t. 24 bit reload value.

Definition at line 55 of file systick.c.

References STK_RVR, and STK_RVR_RELOAD.

Referenced by systick_set_frequency().

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